Attenuated superactive multimetallic catalytic composite

ABSTRACT

A novel attenuated superactive multimetallic catalytic composite especially useful for converting hydrocarbons comprises a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of catalytically effective amounts of a platinum group component, which is maintained in the elemental metallic state, and of a tantalum component. In a highly preferred embodiment, this novel catalytic composite also contains a catalytically effective amount of a halogen component. The platinum group component, pyrolyzed rhenium carbonyl component, tantalum component and optional halogen component are preferably present in the multimetallic catalytic composite in amounts, calculated on an elemental basis, corresponding to about 0.01 to about 2 wt. % platinum group metal, about 0.01 to about 5 wt. % rhenium, about 0.01 to about 5 wt. % tantalum and about 0.1 to about 3.5 wt. % halogen. A key feature associated with the preparation of the subject catalytic composite is reaction of a rhenium carbonyl complex with a porous carrier material containing a uniform dispersion of a tantalum component and of a platinum group metal maintained in the elemental state, whereby the interaction of the rhenium moiety with the platinum group moiety is maximized due to the platinophilic (i.e. platinum-seeking) propensities of the carbon monoxide ligand used in the rhenium reagent.

CROSS-REFERENCES TO RELATED DISCLOSURES

This application is a division of my prior, copending application Ser.No. 910,301 filed May 26, 1978, now U.S. Pat. No. 4,159,939, which inturn is a continuation-in-part of my prior, copending application Ser.No. 833,332 filed Sept. 14, 1977, now U.S. Pat. No. 4,165,276. All ofthe teachings of these prior applications are specifically incorporatedherein by reference.

The subject of the present invention is a novel attenuated superactivemultimetallic catalytic composite which has unusual and impressiveactivity, selectivity and resistance to deactivation characteristicswhen employed in a hydrocarbon conversion process that requires acatalytic agent having both a hydrogenation-dehydrogenation function anda carbonium ion-forming function. The present invention, more precisely,involves a novel dual-function attenuated superactive multimetalliccatalytic composite which quite surprisingly enables substantialimprovements in hydrocarbon conversion processes that have traditionallyused a platinum group metal-containing, dual-function catalyst.According to another aspect, the present invention comprehends theimproved processes that are produced by the use of the instantattenuated superactive platinum-rhenium-tantalum catalyst system whichis characterized by a unique reaction between a rhenium carbonylcompound and a porous carrier material containing a uniform dispersionof a tantalum component and of a platinum group component maintained inthe elemental metallic state, whereby the interaction between therhenium moiety and the platinum group moiety is maximized on an atomiclevel. In a specific aspect, the present invention concerns a catalyticreforming process which utilizes the subject catalyst to markedlyimprove C₅ +-selectivity and H₂ -selectivity characteristics associatedtherewith to a degree not heretofore realized for platinum-rhenium orplatinum-tantalum catalyst systems. Key advantages associated with useof the present attenuated superactive platinum-rhenium-tantalum systemin a catalytic reforming process relative to those observed with theprior art platinum-rhenium or platinum-tantalum catalyst systems are:(1) comparable or increased ability to make octane at low severityoperating conditions; and (2) substantially enhanced capability tomaximize C₅ + reformate and hydrogen production.

Composites having a hydrogenation-dehydrogenation function and acarbonium ion-forming function are widely used today as catalysts inmany industries, such as the petroleum and petrochemical industry, toaccelerate a wide spectrum of hydrocarbon conversion reactions.Generally, the carbonium ion-forming function is thought to beassociated with an acid-acting material of the porous, adsorptive,refractory oxide type which is typically utilized as the support orcarrier for a heavy metal component such as the metals or compounds ofmetals of Groups V through VIII of the Periodic Table to which aregenerally attributed the hydrogenation-dehydrogenation function.

These catalytic composites are used to accelerate a wide variety ofhydrocarbon conversion reactions such as hydrocracking, hydrogenolysis,isomerization, dehydrogenation, hydrogenation, desulfurization,cyclization, polymerization, alkylation, cracking, hydroisomerization,dealkylation, transalkylation, etc. In many cases, the commercialapplications of these catalysts are in processes where more than one ofthe reactions are proceeding simultaneously. An example of this type ofprocess is reforming wherein a hydrocarbon feedstream containingparaffins and naphthenes is subjected to conditions which promotedehydrogenation of naphthenes to aromatics, dehydrocyclization ofparaffins to aromatics, isomerization of paraffins and naphthenes,hydrocracking and hydrogenolysis of naphthenes and paraffins, and thelike reactions, to produce an octane-rich or aromatic-rich productstream. Another example is a hydrocracking process wherein catalysts ofthis type are utilized to effect selective hydrogenation and cracking ofhigh molecular weight unsaturated materials, selective hydrocracking ofhigh molecular weight materials, and other like reactions, to produce agenerally lower boiling, more valuable output stream. Yet anotherexample is a hydroisomerization process wherein a hydrocarbon fractionwhich is relatively rich in straight-chain paraffin compounds iscontacted with a dual-function catalyst to produce an output stream richin isoparaffin compounds.

Regardless of the reaction involved or the particular process involved,it is of critical importance that the dual-function catalyst exhibit notonly the capability to initially perform its specified functions, butalso that it has the capability to perform them satisfactorily forprolonged periods of time. The analytical terms used in the art tomeasure how well a particular catalyst performs its intended functionsin a particular hydrocarbon reaction environment are activity,selectivity, and stability. And for purposes of discussion here, theseterms are conveniently defined for a given charge stock as follows: (1)activity is a measure of the catalyst's ability of convert hydrocarbonreactants into products at a specified severity level where severitylevel means the conditions used--that is, the temperature, pressure,contact time, and presence of diluents such as H₂ ; (2) selectivityrefers to the amount of desired product or products obtained relative tothe amount of reactants charged or converted; (3) stability refers tothe rate of change with time of the activity and selectivityparameters-obviously, the smaller rate implying the more stablecatalyst. In a reforming process, for example, activity commonly refersto the amount of conversion that takes place for a given charge stock ata specified severity level and is typically measured by octane number ofthe C₅ + product stream; selectivity refers to the amount of C₅ + yield,relative to the amount of the charge, that is obtained at the particularactivity or severity level; and stability is typically equated to therate of change with time of activity, as measured by octane number ofC₅ + product and of selectivity as measured by C₅ + yield. Actually thelast statement is not strictly correct because generally a continuousreforming process is run to produce a constant octane C₅ + product withseverity level being continuously adjusted to attain this result; andfurthermore, the severity level is for this process usually varied byadjusting the conversion temperature in the reaction so that, in pointof fact, the rate of change of activity finds response in the rate ofchange of conversion temperatures and changes in this last parameter arecustomarily taken as indicative of activity stability.

As is well known to those skilled in the art, the principal cause ofobserved deactivation or instability of a dual-function catalyst when itis used in a hydrocarbon conversion reaction is associated with the factthat coke forms on the surface of the catalyst during the course of thereaction. More specifically, in these hydrocarbon conversion processesthe conditions utilized typically result in the formation of heavy, highmolecular weight, black, solid or semi-solid, carbonaceous materialwhich is a hydrogen-deficient polymeric substance having properties akinto both polynuclear aromatics and graphite. This material coats thesurface of the catalyst and thus reduces its activity by shielding itsactive sites from the reactants. In other words, the performance of thisdual-function catalyst is sensitive to the presence of carbonaceousdeposits or coke on the surface of the catalyst. Accordingly, the majorproblem facing workers in this area of the art is the development ofmore active and/or selective catalytic composites that are not assensitive to the presence of these carbonaceous materials and/or havethe capability to suppress the rate of the formation of thesecarbonaceous materials on the catalyst. Viewed in terms of performanceparameters, the problem is to develop a dual-function catalyst havingsuperior activity, selectivity, and stability characteristics. Inparticular, for a reforming process the problem is typically expressedin terms of shifting and stabilizing the C₅ + yield-octane relationshipat the lowest possible severity level--C₅ + yield being representativeof selectivity and octane being proportional to activity.

BRIEF DESCRIPTION OF DRAWING

FIGS. 1, 2 and 3 of the attached drawing are graphic representations ofthe results obtained in the examples.

I have now found a dual-function attenuated superactive multimetalliccatalytic composite which possesses improved activity, selectivity andstability characteristics relative to similar catalysts of the prior artwhen it is employed in a process for the conversion of hydrocarbons ofthe type which have heretofore utilized dual-function, platinum groupmetal-containing catalytic composites such as processes forisomerization, hydroisomerization, dehydrogenation, desulfurization,denitrogenization, hydrogenation, alkylation, dealkylation,disproportionation, polymerization, hydrodealkylation, transalkylation,cyclization, dehydrocyclization, cracking, hydrocracking, halogenation,reforming and the like processes. In particular, I have now establishedthat an attenuated superactive multimetallic catalytic composite,comprising a combination of a catalytically effective amount of apyrolyzed rhenium carbonyl component with a porous carrier materialcontaining catalytically effective amounts of a platinum group componentand a tantalum component, can enable the performance of hydrocarbonconversion processes utilizing dual-function catalysts to besubstantially improved if the platinum group component is relativelyuniformly dispersed throughout the porous carrier material prior tocontact with the rhenium carbonyl reagent, if the oxidation state of theplatinum group metal is maintained in the elemental metallic state priorto and during contact with the rhenium carbonyl reagent and if hightemperature treatment in the presence of oxygen and/or water of theresulting reaction product is avoided. A specific example of mydiscovery involves my finding that an attenuated superactive acidicmultimetallic catalytic composite, comprising a combination of acatalytically effective amount of a pyrolyzed rhenium carbonyl componentwith a porous carrier material containing a uniform dispersion ofcatalytically effective amounts of a platinum group component maintainedin the elemental metallic state, of a tantalum component and of ahalogen component, can be utilized to substantially improve theperformance of a hydrocarbon reforming process which operates on a lowoctane gasoline fraction to produce a high octane reformate oraromatic-rich reformate. In the case of a reforming process, some of themajor advantages associated with the use of the novel multimetalliccatalytic composite of the present invention include: (1) acquisition ofthe capability to operate in a stable manner in a high severityoperation; for example, a low or moderate pressure reforming processdesigned to produce a C₅ + reformate having an octane of at least about100 F-1 clear; (2) comparable or increased activity for octane-upgradingreactions relative to the performance of (a) prior art bimetallicplatinum-rhenium catalyst system as exemplified by the teachings ofKluksdahl in his U.S. Pat. No. 3,415,737; and (b) prior art bimetallicplatinum-tantalum catalyst systems as shown in the teachings of U.S.Pat. No. 3,799,867; and (3) substantially increased capability tomaximize C₅ + yield and hydrogen production relative to these prior artcatalyst systems. In sum, the present invention involves the remarkablefinding that the addition of a pyrolyzed rhenium carbonyl component to aporous carrier material containing a uniform dispersion of acatalytically effective amount of a platinum group component maintainedin the elemental metallic state and of a tantalum component, can enablethe performance characteristics of the resulting attenuated superactivemultimetallic catalytic composite to be sharply and materially improvedrelative to those associated with the prior art platinum-rhenium andplatinum-tantalum catalyst systems.

It is accordingly, an object of the present invention to provide anattenuated superactive multimetallic hydrocarbon conversion catalysthaving superior performance characteristics relative to the prior artplatinum-rhenium and platinum-tantalum catalyst systems when utilized ina hydrocarbon conversion process. A second object is to provide anattenuated superactive multimetallic acidic catalyst havingdual-function hydrocarbon conversion performance characteristics whichare relatively insensitive to the deposition of coke-forming,hydrocarbonaceous materials thereon and to the presence of sulfurcontaminants in the reaction environment. A third object is to providepreferred methods of preparation of this attenuated superactivemultimetallic catalytic composite which methods insure the achievementand maintenance of its unique properties. Another object is to provide asubstantially improved platinum-tantalum catalyst system having superioractivity, selectivity and stability characteristics relative to theplatinum-tantalum catalyst system of the prior art. Another object is toprovide a novel acidic multimetallic hydrocarbon conversion catalystwhich utilizes a pyrolyzed rhenium carbonyl component to beneficallyinteract with and selectively promote an acidic catalyst containing atantalum component, a halogen component and a uniform dispersion of aplatinum group component maintained in the metallic state.

Without the intention of being limited by the following explanation, Ibelieve my discovery that rhenium carbonyl can, quite unexpectedly, beused under the circumstances described herein to synthesize an entirelynew type of platinum-rhenium-tantalum catalyst system, is attributableto one or more unusual and unique routes to greater platinum-rheniuminteraction that are opened or made available by the novel chemistryassociated with the reaction of a rhenium carbonyl reactant with asupported, uniformly dispersed platinum metal. Before considering indetail each of these possible routes to greater platinum-rheniuminteraction it is important to understand that: (1) "Platinum" is usedherein to mean any one of the platinum group metals; (2) The unexpectedresults achieved with my catalyst systems are measured relative to theconventional platinum-rhenium and platinum-tantalum catalyst systems astaught in, for example, the Kluksdahl U.S. Pat. No. 3,415,737 and theCardwell, et al. U.S. Pat. No. 3,799,867; (3) The expression "rheniummoiety" is intended to mean the catalytically active form of the rheniumentity derived from the rhenium carbonyl component in the catalystsystem; and (4) Metallic carbonyls have been suggested generally in theprior art for use in making catalysts such as in U.S. Pat. Nos.3,591,649; 4,048,110 and 2,798,051, but no one to my knowledge has eversuggested using these reagents in the platinum-rhenium orplatinum-tantalum catalyst systems, particularly where substantially allof the platinum component of the catalyst is present in a reduced form(i.e. the metal) prior to incorporation of the rhenium carbonylcomponent. One route to greater platinum-rhenium interaction enabled bythe present invention comes from the theory that the effect of rheniumon a platinum catalyst is very sensitive to the particle size of therhenium moiety; since in my procedure the rhenium is put on the catalystin a form where it is complexed with a carbon monoxide molecule which isknown to have a strong affinity for platinum, it is reasonable to assumethat when the platinum is widely dispersed on the support, one effect ofthe CO ligand is to pull the rhenium moiety towards the platinum siteson the catalyst, thereby achieving a dispersion and particle size of therhenium moiety in the catalyst which closely imitates the correspondingplatinum conditions (i.e. this might be called a piggy-back theory). Thesecond route to greater platinum-rhenium interaction is similar to thefirst and depends on the theory that the effect of rhenium on a platinumcatalyst is at a maximum when the rhenium moiety is attached toindividual platinum sites, the use of platinophilic CO ligands, ascalled for by the present invention, then acts to facilitate adsorptionor chemisorption of the rhenium moiety on the platinum site so that asubstantial portion of the rhenium moiety is deposited or fixed on ornear the platinum site where the platinum acts to anchor the rhenium,thereby making it more resistant to sintering at high temperature. Thethird route to greater platinum-rhenium interaction is based on thetheory that the active state for the rhenium moiety in therhenium-platinum catalyst system is the elemental metallic state andthat the best platinum-rhenium interaction is achieved when theproportion of the rhenium in the metallic state is maximized; using arhenium carbonyl compound to introduce the rhenium into the catalyticcomposite conveniently ensures availability of more rhenium metalbecause all of the rhenium in this reagent is present in the elementalmetallic state. Another route to greater platinum-rhenium interaction isderived from the theory that oxygen at high temperature is detrimentalto both the active form of the rhenium moiety (i.e., the metal) and thedispersion of same on the support (i.e. oxygen at high temperatures issuspected of causing sintering of the rhenium moiety); since thecatalyst of the present invention is not subject to high temperaturetreatment with oxygen after rhenium is incorporated, maximumplatinum-rhenium interaction is obviously preserved. The final theoryfor explaining the greater platinum-rhenium interaction associated withthe instant catalyst is derived from the idea that the active sites forthe platinum-rhenium catalyst are basically platinum metal crystallitesthat have had their surface enriched in rhenium metal; since the conceptof the present invention requires the rhenium to be laid down on thesurface of well-dispersed platinum crystallites via platinophilicrhenium carbonyl complex, the probability of surface enrichment isgreatly increased for the present procedure relative to that associatedwith the random, independent dispersion of both crystallites that hascharacterized the prior art preparation procedures. It is of course tobe recognized that all of these factors may be involved to some degreein the overall explanation of the impressive results associated with myattenuated superactive catalyst system.

Against this background then, the present invention is in oneembodiment, a novel trimetallic catalytic composite comprising acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous material containing a uniformdispersion of catalytically effective amounts of a platinum groupcomponent maintained in the elemental metallic state and of a tantalumcomponent.

In another embodiment, the subject catalytic composite comprises acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous carrier material containing acatalytically effective amount of a halogen component and a uniformdispersion of catalytically effective amounts of a platinum groupcomponent maintained in the elemental metallic state and of a tantalumcomponent.

In yet another embodiment the present invention involves a combinationof a pyrolyzed rhenium carbonyl component with a porous carrier materialcontaining a halogen component and a uniform dispersion of a platinumgroup component maintained in the elemental metallic state and of atantalum component, wherein these components are present in amountssufficient to result in the composite containing, calculated on anelemental basis, about 0.01 to about 2 wt. % platinum group metal, about0.01 to about 5 wt. % rhenium, about 0.01 to about 5 wt. % tantalum, andabout 0.1 to about 3.5 wt. % halogen.

In still another embodiment, the present invention comprises any of thecatalytic composites defined in the previous embodiments wherein theporous carrier material contains, prior to the addition of the pyrolyzedrhenium carbonyl component, not only a platinum group component and atantalum component but also a catalytically effective amount of acomponent selected from the group consisting of tin, lead, germanium,cobalt, nickel, iron, tungsten, chromium, molybdenum, bismuth, indium,gallium, cadmium, zinc, uranium, copper, silver, gold, one or more ofthe rare earth metals and mixtures thereof.

In another aspect, the invention is defined as a catalytic compositecomprising the pyrolyzed reaction product formed by reacting acatalytically effective amount of a rhenium carbonyl compound or complexwith a porous carrier material containing a uniform dispersion ofcatalytically effective amounts of a platinum group metal maintained inthe elemental metallic state and of a tantalum component, and thereaftersubjecting the resulting reaction product to pyrolysis conditionsselected to decompose the rhenium carbonyl component.

An ancillary embodiment of the present invention involves a method ofpreparing any of the catalytic composites defined by the previousembodiments, the method comprising the steps of: (a) reacting a rheniumcarbonyl compound with a porous carrier material containing a uniformdispersion of a platinum group component maintained in the elementalmetallic state and of a tantalum component, and thereafter, (b)subjecting the resulting reaction product to pyrolysis conditionsselected to decompose the rhenium carbonyl component, without oxidizingeither the platinum group or rhenium components.

A further embodiment involves a process for the conversion of ahydrocarbon which comprises contacting the hydrocarbon and hydrogen withthe attenuated superactive catalytic composite defined in any of theprevious embodiments at hydrocarbon conversion conditions.

A highly preferred embodiment comprehends a process for reforming agasoline fraction which comprises contacting the gasoline fraction andhydrogen with the attenuated superactive multimetallic catalyticcomposites defined in any one of the prior embodiments at reformingconditions selected to produce a high octane reformate.

An especially preferred embodiment is a process for the production ofaromatic hydrocarbons which comprises contacting a hydrocarbon fractionrich in aromatic precursors and hydrogen with an acidic catalyticcomposite comprising a combination of a catalytically effective amountof a pyrolyzed rhenium carbonyl component with a porous carrier materialcontaining catalytically effective amounts of a halogen component and ofa tantalum component, and a uniform dispersion of a catalyticallyeffective amount of a platinum group component maintained in theelemental metallic state. This contacting is performed at aromaticproduction conditions selected to produce an effluent stream rich inaromatic hydrocarbons.

Other objects and embodiments of the present invention relate toadditional details regarding the essential and preferred catalyticingredients, preferred amounts of ingredients, appropriate methods ofcatalyst preparation, operating conditions for use with the novelcatalyst in the various hydrocarbon conversion processes in which it hasutility, and the like particulars, which are hereinafter given in thefollowing detailed discussion of each of the essential and preferredfeatures of the present invention.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high surface area support having a surface area of about 25 to about500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon conversion process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts such as: (1) activated carbon, coke, orcharcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc., (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic alumino-silicates suchas naturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, CaAl₂ O₄, and other like compounds having the formulaMO--Al₂ O₃ where M is a metal having a valence of 2; and (7)combinations of elements from one or more of these groups. The preferredporous carrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas gamma-, eta-, and theta-alumina, with gamma- or eta-alumina givingbest results. In addition, in some embodiments the alumina carriermaterial may contain minor proportions of other well known refractoryinorganic oxides such as silica, zirconia, magnesia, etc.; however, thepreferred support is substantially pure gamma- or eta-alumina. Preferredcarrier materials have an apparent bulk density of about 0.3 to about0.8 g/cc and surface area characteristics such that the average porediameter is about 20 to 300 Angstroms, the pore volume is about 0.1 toabout 1 cc/g and the surface area is about 100 to about 500 m² /g. Ingeneral, best results are typically obtained with a gamma-aluminacarrier material which is used in the form of spherical particleshaving: a relatively small diameter (i.e. typically about 1/16 inch), anapparent bulk density of about 0.3 to about 0.8 g/cc. a pore volume ofabout 0.4 ml/g. and a surface area of about 150 to about 250 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere, and alumina spheres may becontinuously manufactured by the well known oil drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting aluminum metal with hydrochloricacid, combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° F.to about 400° F. and subjected to a calcination procedure at atemperature of about 850° F. to about 1300° F. for a period of about 1to about 20 hours. This treatment effects conversion of the aluminahydrogel to the corresponding crystalline gamma-alumina. See theteachings of U.S. Pat. No. 2,620,314 for additional details.

Another particularly preferred alumina carrier material is synthesizedfrom a unique crystalline alumina powder which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a byproduct from a Zieglerhigher alcohol synthesis reaction as described in Ziegler's U.S. Pat.No. 2,892,858. For purposes of simplification, the name "Ziegleralumina" is used herein to identify this material. It is presentlyavailable from the Conoco Chemical Division of Continental Oil Companyunder the trademark Catapal. This material is an extremely high purityalpha-alumina monohydrate (boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina. It iscommercially available in three forms: (1) Catapal SB--a spray driedpowder having a typical surface area of 250 m² /g; (2) Catapal NG--arotary kiln dried alumina having a typical surface area of 180 m² /g;and (3) Dispal M--a finely divided dispersable product having a typicalsurface area of about 185 m² /g. For purposes of the present invention,the preferred starting material is the spray dried powder, Catapal SB.This alpha-alumina monohydrate powder may be formed into a suitablecatalyst material according to any of the techniques known to thoseskilled in the catalyst carrier material forming art. Spherical carriermaterial particles can be formed, for example, from this Ziegler aluminaby: (1) converting the alpha-alumina monohydrate powder into an aluminasol by reaction with a suitable peptizing agent and water and thereafterdropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are easilyconverted to a gamma-alumina carrier material by known methods; (2)forming an extrudate from the powder by established methods andthereafter rolling the extrudate particles on a spinning disc untilspherical particles are formed which can then be dried and calcined toform the desired particles of spherical carrier material; and (3)wetting the powder with a suitable peptizing agent and thereafterrolling particles of the powder into spherical masses of the desiredsize in much the same way that children have been known to make parts ofsnowmen by rolling snowballs down hills covered with wet snow. Thisalumina powder can also be formed in any other desired shape or type ofcarrier material known to those skilled in the art such as rods, pills,pellets, tablets, granules, extrudates and the like forms by methodswell known to the practitioners of the catalyst carrier material formingart. The preferred type of carrier material for the present invention isa cylindrical extrudate having a diameter of about 1/32" to about 1/2"(especially about 1/16") and a length to diameter (L/D) ratio of about1:1 to about 5:1, with a L/D ratio of about 2:1 being especiallypreferred. The especially preferred extrudate form of the carriermaterial is preferably prepared by mixing the alumina powder with waterand a suitable peptizing agent such as nitric acid, acetic acid,aluminum nitrate and the like material until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss on ignition (LOI) at 500° C. of about 45 to 65wt. %, with a value of about 55 wt. % being especially preferred. On theother hand, the acid addition rate is generally sufficient to provideabout 2 to 7 wt. % of the volatile free alumina powder used in the mix,with a value of about 3 to 4% being especially preferred. The resultingdough is then extruded through a suitably sized die to form extrudateparticles. These particles are then dried at a temperature of about 500°to 800° F. for a period of about 0.1 to about 5 hours and thereaftercalcined at a temperature of about 900° F. to about 1500° F. for aperiod of about 0.5 to about 5 hours to form the preferred extrudateparticles of the Ziegler alumina carrier material. In addition, in someembodiments of the present invention the Ziegler alumina carriermaterial may contain minor proportions of other well known refractoryinorganic oxides such as silica, titanium dioxide, zirconium dioxide,chromium oxide, beryllium oxide, vanadium oxide, cesium oxide, hafniumoxide, zinc oxide, iron oxide, cobalt oxide, magnesia, boria, thoria,and the like materials which can be blended into the extrudable doughprior to the extrusion of same. In the same manner crystalline zeoliticaluminosilicates such as naturally occurring or synthetically preparedmordenite and/or faujasite, either in the hydrogen form or in a formwhich has been treated with a multivalent cation, such as a rare earth,can be incorporated into this carrier material by blending finelydivided particles of same into the extrudable dough prior to extrusionof same. A preferred carrier material of this type is substantially pureZiegler alumina having an apparent bulk density (ABD) of about 0.6 to 1g/cc (especially an ABD of about 0.7 to about 0.85 g/cc), a surface areaof about 150 to about 280 m² /g (preferably about 185 to about 235 m²/g,) and a pore volume of about 0.3 to about 0.8 cc/g.

A first essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as afirst component of the attenuated superactive catalytic composite. It isan essential feature of the present invention that substantially all ofthis platinum group component is uniformly dispersed throughout theporous carrier material in the elemental metallic state prior to theincorporation of the rhenium carbonyl ingredient. Generally, the amountof this component present in the form of catalytic composites is smalland typically will comprise about 0.01 to about 2 wt % of finalcatalytic composite, calculated on an elemental basis. Excellent resultsare obtained when the catalyst contains about 0.05 to about 1 wt. % ofplatinum, iridium, rhodium, palladium or ruthenium metal. Particularlypreferred mixtures of these platinum group metals preferred for use inthe composite of the present invention are: (1) platinum and iridium,(2) platinum and rhodium, and (3) platinum and ruthenium.

This platinum group component may be incorporated into the porouscarrier material in any suitable manner known to result in a relativelyuniform distribution of this component in the carrier material such ascoprecipitation or cogelation, ion-exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlorohodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of a platinum, iridium, rhodium,or palladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is preferred sinceit facilitates the incorporation of both the platinum group componentand at least a minor quantity of the preferred halogen component in asingle step. Hydrogen chloride or the like acid is also generally addedto the impregnation solution in order to further facilitate theincorporation of the halogen component and the uniform distribution ofthe metallic components throughout the carrier material. In addition, itis generally preferred to impregnate the carrier material after it hasbeen calcined in order to minimize the risk of washing away the valuableplatinum group compound.

A second essential constituent of the novel multimetallic catalyst ofthe present invention is a tantalum component. This component may ingeneral be present in the instant catalytic composite in anycatalytically available form in which the tantalum moiety is present ina positive oxidation state such as a compound like the oxide, hydroxide,halide, oxyhalide, aluminate, or in chemical combination with one ormore of the other ingredients of the catalyst. Although it is notintended to restrict the present invention by this explanation, it isbelieved that best results are obtained when the tantalum component ispresent in the composite in the form of tantalum oxide or tantalumaluminate, or tantalum oxyhalide or a mixture thereof, and thesubsequently described oxidation and reduction steps that are preferablyused in the preparation of the instant catalytic composite arespecifically designed to achieve this end. The term "tantalum aluminate"as used herein refers to a coordinated complex of tantalum, oxygen, andaluminum which are not necessarily present in the same relationship forall cases covered herein. this tantalum component can be used in anyamount which is catalytically effective, with good results obtained, onan elemental basis, with about 0.01 to about 5 wt. % tantalum in thecatalyst. Best results are ordinarily achieved with about 0.05 to about1 wt. % tantalum, calculated on an elemental basis, and with an atomicratio of tantalum to platinum group metal of about 0.1:1 to 10:1,especially about 0.5:1 to 5:1.

This tantalum component may be incorporated into the porous carriermaterial in any suitable manner known to the art to result in arelatively uniform dispersion of the tantalum moiety in the carriermaterial, such as by coprecipitation or cogellation or coextrusion withthe porous carrier material, ion exchange with the gelled carriermaterial, or impregnation of the carrier material either after, before,or during the period when it is dried and calcined. It is to be notedthat it is intended to include within the scope of the present inventionall conventional methods for incorporating and simultaneously uniformlydistributing a metallic component in a catalyst composite and theparticular method of incorporation used is not deemed to be an essentialfeature of the present invention. One especially preferred method ofincorporating the tantalum component into the porous carrier materialinvolves cogelling, coextrusion, or coprecipitating the tantalumcomponent in the form of the corresponding halide or oxyhalide orhydrous oxide during the preparation of the preferred carrier material,alumina. This method typically involves the addition of a suitablesol-soluble or sol-dispersable tantalum compound such as finely dividedtantalum pentachloride or tantalum pentoxide hydrate and the like to thealumina hydrosol and then combining the hydrosol with a suitable gellingagent and dropping the resulting mixture into an oil bath, etc., asexplained in detail hereinbefore. Alternatively, the finely dividedtantalum compound can be added to the gelling agent. After drying andcalcining the resulting gelled carrier material in air, there isobtained an intimate combination of alumina and tantalum oxide and/oroxyhalide and/or aluminate. Another method of incorporating the tantalumcomponent into the porous carrier material involves utilization of asoluble, decomposable compound of tantalum to impregnate the porouscarrier material. In general, the solvent used in this impregnation stepis selected on the basis of the capability to dissolve the desiredtantalum compound without adversely affecting the carrier material orthe other ingredients of the catalyst--for example, a suitable alcohol,ether, acid and the like solvents. The solvent is preferably an absolutealcohol or an aqueous, strongly acidic solution. Thus, the tantalumcomponent may be added to the carrier material by commingling the latterwith a solution of suitable tantalum salt, complex, or compound such astantalum pentabromide, tantalum pentachloride, tantalum pentafluoride,tantalum pentoxide hydrate (also known as tantalic acid), tantalumoxytrichloride, the oxalic and tartaric complexes of tantalic acid, anyof the soluble tantalate salts such as potassium fluorotantalate orpotassium tantalate, and the like compounds. A particularly preferredimpregnation solution comprises an absolute alcohol solution of tantalumpentachloride. In general, the tantalum component can be added to thecarrier material either prior to, simultaneously with, or after theplatinum group component is added to the carrier material. However,excellent results are obtained when the tantalum component is added tothe carrier material prior to the platinum group component.

It is especially preferred to incorporate a halogen component into theplatinum group metal-and tantalum-containing porous carrier materialprior to the reactions thereof with the rhenium carbonyl reagent.Although the precise form of the chemistry of the association of thehalogen component with the carrier material is not entirely known, it iscustomary in the art to refer to the halogen component as being combinedwith the carrier material or with the platinum group and/or tantalumcomponents in the form of the halide (e.g. as the chloride). Thiscombined halogen may be either fluorine, chlorine, iodine, bromine, ormixtures thereof. Of these, fluorine and, particularly, chlorine arepreferred for the purposes of the present invention. The halogen may beadded to the carrier material in any suitable manner, either duringpreparation of the support or before or after the addition of theplatinum group and tantalum components. For example, the halogen may beadded, at any stage of the preparation of the carrier material or to thecalcined carrier material, as an aqueous solution of a suitable,decomposable halogen-containing compound such as hydrogen fluoride,hydrogen chloride, hydrogen bromide, ammonium chloride, etc. The halogencomponent or a portion thereof, may be combined with the carriermaterial during the impregnation of the latter with the platinum groupand/or tantalum components, for example, through the utilization of amixture of chloroplatinic acid and hydrogen chloride. In anothersituation, the alumina hydrosol which is typically utilized to form apreferred alumina carrier material may contain halogen and thuscontribute at least a portion of the halogen component to the finalcomposite. For reforming, the halogen will be typically combined withthe carrier material in an amount sufficient to result in a finalcomposite that contains about 0.1 to about 3.5%, and preferably about0.5 to about 1.5%, by weight of halogen, calculated on an elementalbasis. In isomerization or hydrocracking embodiments, it is generallypreferred to utilize relatively larger amounts of halogen in thecatalyst--typically, ranging up to about 10 wt. % halogen calculated onan elemental basis, and more preferably, about 1 to about 5 wt. %. It isto be understood that the specified level of halogen component in theinstant attenuated superactive catalyst can be achieved or maintainedduring use in the conversion of hydrocarbons by continuously orperiodically adding to the reaction zone a decomposablehalogen-containing compound such as an organic chloride (e.g. ethylenedichloride, carbon tetrachloride, t-butyl chloride) in an amount ofabout 1 to 100 wt. ppm. of the hydrocarbon feed, and preferably about 1to 10 wt. ppm.

After the platinum group and tantalum components are combined with theporous carrier material, the resulting platinum group metal-andtantalum-containing carrier material will generally be dried at atemperature of about 200° F. to about 600° F. for a period of typicallyabout 1 to about 24 hours or more and thereafter oxidized at atemperature of about 700° F. to about 1100° F. in an air or oxygenatmosphere for a period of about 0.5 to about 10 or more hours ofconverts substantially all of the platinum group and tantalum componentsto the corresponding metallic oxides. When the preferred halogencomponent is utilized in the present composition, best results aregenerally obtained when the halogen content of the platinum groupmetal-and tantalum-containing carrier material is adjusted during thisoxidation step by including a halogen or a halogen-containing compoundin the air or oxygen atmosphere utilized. For purposes of the presentinvention, the particularly preferred halogen is chlorine and it ishighly recommended that the halogen compound utilized in thishalogenation step be either hydrochloric acid or a hydrochloric acidproducing substance. In particular, when the halogen component of thecatalyst is chlorine, it is preferred to use a molar ratio of H₂ O toHCl of about 5:1 to about 100:1 during at least a portion of theoxidation step which follows the platinum group metal impregnation inorder to adjust the final chlorine content of the catalyst to a range ofabout 0.1 to about 3.5 wt. %. Preferably, the duration of thishalogenation step is about 1 to 5 or more hours.

A crucial feature of the present invention involves subjecting theresulting oxidized, platinum group metal-and tantalum-containing, andtypically halogen-treated, carrier material to a substantiallywater-free reduction step before the incorporation of the rheniumcomponent by means of the rhenium carbonyl reagent. The importance ofthis reduction step comes from my observation that when an attempt ismade to prepare the instant catalytic composite without first reducingthe platinum group component, no significant improvement in theplatinum-rhenium-tantalum catalyst system is obtained; put another way,it is my finding that it is essential for the platinum group componentto be well dispersed in the porous carrier material in the elementmetallic state prior to incorporation of the rhenium component by theunique procedure of the present invention in order for synergisticinteraction of the rhenium carbonyl with the dispersed platinum groupmetal to occur according to the theories that I have previouslyexplained. Accordingly, this reduction step is designed to reducesubstantially all of the platinum group component to the elementalmetallic state and to assure a relatively uniform and finely divideddispersion of this metallic component throughout the porous carriermaterial. Preferably a substantially pure and dry hydrogen stream (bythe use of the word "dry" I mean that it contains less than 20 vol. ppmwater and preferably less than 5 vol. ppm water) is used as the reducingagent in this step. The reducing agent is contacted with the oxidized,platinum group metal-and tantalum-containing carrier material atconditions including a reduction temperature of about 450° F. to about1200° F. for a period of about 0.5 to about 10 or more hours selected toreduce substantially all of the platinum group component to theelemental metallic state. Once this condition of finely divideddispersed platinum group metal in the porous carrier material isachieved, it is important that environments and/or conditions that coulddisturb or change this condition be avoided; specifically, I much preferto maintain the freshly reduced carrier material containing the platinumgroup metal under a blanket of inert gas to avoid any possibility ofcontamination of same either by water or by oxygen.

A third essential ingredient of the present attenuated superactivecatalytic composite is a rhenium component which I have chosen tocharacterize as a pyrolyzed rhenium carbonyl in order to emphasize thatthe rhenium moiety of interest in my invention is the rhenium producedby decomposing a rhenium carbonyl in the presence of a finely divideddispersion of a platinum group metal and in the absence of materialssuch as oxygen or water which could interfere with the basic desiredinteraction of the rhenium carbonyl component with the platinum groupmetal component as previously explained. In view of the fact that all ofthe rhenium contained in a rhenium carbonyl compound is present in theelemental metallic state, an essential requirement of my invention isthat the resulting reaction product of the rhenium carbonyl compound orcomplex with the platinum group metal-and tantalum-loaded carriermaterial is not subjected to conditions which could in any way interferewith the maintenance of the rhenium moiety in the elemental metallicstate; consequently, avoidance of any conditions which would tend tocause the oxidation of any portion of the rhenium ingredient or of theplatinum gtoup ingredient is a requirement for full realization of thesynergistic interaction enabled by the present invention. This rheniumcomponent may be utilized in the resulting composite in any amount thatis catalytically effective with the preferred amount typicallycorresponding to about 0.01 to about 5 wt. % thereof, calculated on anelemental rhenium basis. Best results are ordinarily obtained with about0.05 to about 1 wt. % rhenium. The traditional rule for rhenium-platinumcatalyst system is that best results are achieved when the amount of therhenium component is set as a function of the amount of the platinumgroup component also hold for my composition; specifically, I find thatbest results with a rhenium to platinum group metal atomic ratio ofabout 0.1:1 to about 10:1, with an especially useful range comprisingabout 0.2:1 to about 5:1 and with superior results achieved at an atomicratio of rhenium to platinum group metal of about 1:1. The rheniumcarbonyl ingredient may be reacted with the reduced platinum groupmetal-and tantalum-containing porous carrier material in any suitablemanner known to those skilled in the catalyst formulation art whichresults in relatively good contact between the rhenium carbonyl complexand the platinum group component contained in the porous carriermaterial. One acceptable procedure for incorporating the rheniumcarbonyl compound into the composite involves sublimating the rheniumcarbonyl complex under conditions which enable it to pass into the vaporphase without being decomposed and thereafter contacting the resultingrhenium carbonyl sublimate with the platinum group metal-andtantalum-containing porous carrier material under conditions designed toachieve intimate contact of the carbonyl reagent with the platinum groupmetal dispersed on the carrier material. Typically this procedure isperformed under vacuum at a temperature of about 70° to about 250° F.for a period of time sufficient to react the desired amount of rheniumwith the carrier material. In some cases, an inert carrier gas such asnitrogen can be admixed with the rhenium carbonyl sublimate in order tofacilitate the intimate contacting of same with the platinum-andtantalum-loaded porous carrier material. A particularly preferred way ofaccomplishing this rhenium carbonyl reaction step is an impregnationprocedure wherein the platinum-and tantalum-loaded porous carriermaterial is impregnated with a suitable solution containing the desiredquantity of the rhenium carbonyl complex. For purposes of the presentinvention, organic solutions are preferred, although any suitablesolution may be utilized as long as it does not interact with therhenium carbonyl and cause decomposition of same. Obviously the organicsolution should be anhydrous in order to avoid detrimental interactionof water with the rhenium carbonyl compound. Suitable solvents are anyof the commonly available organic solvents such as one of the availableethers, alcohols, ketones, aldehydes, paraffins, naphthenes and aromatichydrocarbons, for example, acetone, acetyl acetone, benzaldehyde,pentane, hexane, carbon tetrachloride, methyl isopropyl ketone, benzene,n-butylether, diethyl ether, ethylene glycol, methyl isobutyl ketone,diisobutyl ketone and the like organic solvents. Best results areordinarily obtained when the solvent is acetone; consequently, thepreferred impregnation solution is rhenium carbonyl dissolved inanhydrous acetone. The rhenium carbonyl complex suitable for use in thepresent invention may be either the pure rhenium carbonyl itself or asubstituted rhenium carbonyl such as the rhenium carbonyl halidesincluding the chlorides, bromides, and iodides and the like substitutedrhenium carbonyl complexes. After impregnation of the carrier materialwith the rhenium carbonyl component, it is important that the solvent beremoved or evaporated from the catalyst prior to decomposition of therhenium carbonyl component by means of the hereinafter describedpyrolysis step. The reason for removal of the solvent is that I believethat the presence of organic materials such as hydrocarbons orderivatives of hydrocarbons during the rhenium carbonyl pyrolysis stepis highly detrimental to the synergistic interaction associated with thepresent invention. This solvent is removed by subjecting the rheniumcarbonyl impregnated carrier material to a temperature of about 100° F.to about 250° F. in the presence of an inert gas or under a vacuumcondition until substantially no further solvent is observed to come offthe impregnated material. In the preferred case where acetone is used asthe impregnation solvent, this drying of the impregnated carriermaterial typically takes about one half hour at a temperature of about225° F. under moderate vacuum conditions.

After the rhenium carbonyl component is incorporated into theplatinum-and-tantalum-loaded porous carrier material, the resultingcomposite is, pursuant to the present invention, subjected to pyrolysisconditions designed to decompose substantially all of the rheniumcarbonyl material, without oxidizing either the platinum group or thedecomposed rhenium carbonyl component. This step is preferably conductedin an atmosphere which is substantially inert to the rhenium carbonylsuch as in a nitrogen or noble gas-containing atmosphere. Preferablythis pyrolysis step takes place in the presence of a substantially pureand dry hydrogen stream. It is of course within the scope of the presentinvention to conduct the pyrolysis step under vacuum conditions. It ismuch preferred to conduct this step in the substantial absence of freeoxygen and substances that could yield free oxygen under the conditionsselected. Likewise it is clear that best results are obtained when thisstep is performed in the total absence of water and of hydrocarbons andother organic materials. I have obtained best results in pyrolyzingrhenium carbonyl while using an anhydrous hydrogen stream at pyrolysisconditions including a temperature of about 300° F. to about 900° F. ormore, preferably about 400° F. to about 750° F., a gas hourly spacevelocity of about 250 to about 1500 hr.⁻¹ for a period of about 0.5 toabout 5 or more hours until no further evolution of carbon monoxide isnoted. After the rhenium carbonyl component has been pyrolyzed, it is amuch preferred practice to maintain the resulting catalytic composite inan inert environment (i.e. a nitrogen or the like inert gas blanket)until the catalyst is loaded into a reaction zone for use in theconversion of hydrocarbons.

The resulting pyrolyzed catalytic composite may, in some cases, bebeneficially subjected to a presulfiding step designed to incorporate inthe catalytic composite from about 0.01 to about 1 wt. % sulfurcalculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitabledecomposable sulfur-containing compound such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the pyrolyzed catalyst with a sulfiding gassuch as a mixture of hydrogen and hydrogen sulfide containing about 10moles of hydrogen per mole of hydrogen sulfide at conditions sufficientto effect the desired incorporation of sulfur, generally including atemperature ranging from about 50° F. up to about 1000° F. It isgenerally a preferred practice to perform this presulfiding step undersubstantially water-free and oxygen-free conditions. It is within thescope of the present invention to maintain or achieve the sulfided stateof the present catalyst during use in the conversion of hydrocarbons bycontinuously or periodically adding a decomposable sulfur-containingcompound, selected from the above-mentioned hereinbefore, to the reactorcontaining the attenuated superactive catalyst in an amount sufficientto provide about 1 to 500 wt. ppm., preferably about 1 to about 20 wt.ppm. of sulfur, based on hydrocarbon charge. According to another modeof operation, this sulfiding step may be accomplished during thepyrolysis step by utilizing a rhenium carbonyl reagent which has asulfur-containing ligand or by adding H₂ S to the hydrogen stream whichis preferably used therein.

In embodiments of the present invention wherein the instant attenuatedsuperactive multimetallic catalytic composite is used for thedehydrogenation of dehydrogenatable hydrocarbons or for thehydrogenation of hydrogenatable hydrocarbons, it is ordinarily apreferred practice to include an alkali or alkaline earth metalcomponent in the composite before addition to the rhenium carbonylcomponent and to minimize or eliminate the preferred halogen component.More precisely, this optional ingredient is selected from the groupconsisting of the compounds of the alkali metals--cesium, rubidium,potassium, sodium, and lithium--and the compounds of the alkaline earthmetals--calcium, strontium, barium, and magnesium. Generally, goodresults are obtained in these embodiments when this componentconstitutes about 0.1 to about 5 wt. % of the composite, calculated onan elemental basis. This optional alkali or alkaline earth metalcomponent can be incorporated into the composite in any of the knownways, with impregnation with an aqueous solution of a suitablewater-soluble, decomposable compound being preferred.

An optional ingredient for the attenuated superactive multimetalliccatalyst of the present invention is a Friedal-Crafts metal halidecomponent. This ingredient is particularly useful in hydrocarbonconversion embodiments of the present invention wherein it is preferredthat the catalyst utilized has a strong acid or cracking functionassociated therewith--for example, an embodiment wherein thehydrocarbons are to be hydrocracked or isomerized with the catalyst ofthe present invention. Suitable metal halides of the Friedel-Crafts typeinclude aluminum chloride, aluminum bromide, ferric chloride, ferricbromide, zinc chloride, and the like compounds, with the aluminumhalides and particularly aluminum chloride ordinarily yielding bestresults. Generally, this optional ingredient can be incorporated intothe composite of the present invention by any of the conventionalmethods for adding metallic halides of this type and either prior to orafter the rhenium carbonyl reagent is added thereto; however, bestresults are ordinarily obtained when the metallic halide is sublimedonto the surface of the carrier material after the rhenium is addedthereto according to the preferred method disclosed in U.S. Pat. No.2,999,074. The component can generally be utilized in any amount whichis catalytically effective, with a value selected from the range ofabout 1 to about 100 wt. % of the carrier material generally beingpreferred.

According to the present invention, a hydrocarbon charge stock andhydrogen are contacted with the instant attenuated superactivemultimetallic catalyst in a hydrocarbon conversion zone. This contactingmay be accomplished by using the catalyst in a fixed bed system, amoving bed system, a fluidized bed system, or in a batch type operation;however, in view of the danger of attrition losses of the valuablecatalyst and of well known operational advantages, it is preferred touse either a fixed bed system or a dense-phase moving bed system such asis shown in U.S. Pat. No. 3,725,249. It is also contemplated that thecontacting step can be performed in the presence of a physical mixtureof particles of the catalyst of the present invention and particles of aconventional dual-function catalyst of the prior art. In a fixed bedsystem, a hydrogen-rich gas and the charge stock are preheated by anysuitable heating means to the desired reaction temperature and then arepassed into a conversion zone containing a fixed bed of the attenuatedsuperactive multimetallic catalyst. It is, of course, understood thatthe conversion zone may be one or more separate reactors with suitablemeans therebetween to ensure that the desired converson temperature ismaintained at the entrance to each reactor. It is also important to notethat the reactants may be contacted with the catalyst bed in eitherupward, downward, or radial flow fashion with the latter beingpreferred. In addition, the reactants may be in the liquid phase, amixed liquid-vapor phase, or a vapor phase when they contact thecatalyst, with best results obtained in the vapor phase.

In the case where the attenuated superactive multimetallic catalyst ofthe present invention is used in a reforming operation, the reformingsystem will typically comprise a reforming zone containing one or morefixed beds or dense-phase moving beds of the catalysts. In a multiplebed system, it is, of course, within the scope of the present inventionto use the present catalyst in less than all of the beds with aconventional dual-function catalyst being used in the remainder of thebeds. This reforming zone may be one or more separate reactors withsuitable heating means therebetween to compensate for the endothermicnature of the reactions that take place in each catalyst bed. Thehydrocarbon feed stream that is charged to this reforming system willcomprise hydrocarbon fractions containing naphthenes and paraffins thatboil within the gasoline range. The preferred charge stocks are thoseconsisting essentially of naphthenes and paraffins, although in somecases aromatics and/or olefins may also be present. This preferred classincludes straight run gasolines, natural gasolines, synthetic gasolines,partially reformed gasolines, and the like. On the other hand, it isfrequently advantageous to charge thermally or catalytically crackedgasolines or higher boiling fractions thereof. Mixtures of straight runand cracked gasolines can also be used to advantage. The gasoline chargestock may be a full boiling gasoline having an initial boiling point offrom about 50° F. to about 150° F. and an end boiling point within therange of from about 325° F. to about 425° F., or may be a selectedfraction thereof which generally will be a higher boiling fractioncommonly referred to as a heavy naphtha--for example, a naphtha boilingin the range of C₇ to 400° F. In some cases, it is also advantageous tocharge pure hydrocarbons or mixtures of hydrocarbons that have beenextracted from hydrocarbon distillates--for example, straight-chainparaffins--which are to be converted to aromatics. It is preferred thatthese charge stocks be treated by conventional catalytic pretreatmentmethods such as hydrorefining, hydrotreating, hydrodesulfurization,etc., to remove substantially all sulfurous, nitrogenous, andwater-yielding contaminants therefrom and to saturate any olefins thatmay be contained therein.

In other hydrocarbon conversion embodiments, the charge stock will be ofthe conventional type customarily used for the particular kind ofhydrocarbon conversion being effected. For example, in a typicalisomerization embodiment, the charge stock can be a paraffinic stockrich in C₄ to C₈ normal paraffins, or a normal butane-rich stock, or ann-hexane-rich stock, or a mixture of xylene isomers, or anolefin-containing stock, etc. In a dehydrogenation embodiment, thecharge stock can be any of the known dehydrogenatable hydrocarbons suchas an aliphatic compound containing 2 to 30 carbon atoms per molecule, aC₄ to C₃₀ normal paraffin, a C₈ to C₁₂ alkylaromatic, a naphthene, andthe like. In hydrocracking embodiments, the charge stock will betypically a gas oil, heavy cracked cycle oil, etc. In addition,alkylaromatics, olefins, and naphthenes can be conveniently isomerizedby using the catalyst of the present invention. Likewise, purehydrocarbons or substantially pure hydrocarbons can be converted to morevaluable products by using the acidic multimetallic catalyst of thepresent invention in any of the hydrocarbon conversion processes, knownto the art, that use a dual-function catalyst.

In a reforming embodiment, it is generally preferred to utilize theattenuated superactive multimetallic catalytic composite in asubstantially water-free environment. Essential to the achievement ofthis condition in the reforming zone is the control of the water levelpresent in the charge stock and the hydrogen stream which is beingcharged to the zone. Best results are ordinarily obtained when the totalamount of water entering the conversion zone from any source is held toa level less than 50 ppm. and preferably less than 20 ppm. expressed asweight of equivalent water in the charge stock. In general, this can beaccomplished by careful control of the water present in the charge stockand in the hydrogen stream. The charge stock can be dried by using anysuitable drying means known to the art, such as a conventional solidadsorbent having a high selectivity for water, for instance, sodium orcalcium crystalline aluminosilicates, silica gel, activated alumina,molecular sieves, anhydrous calcium sulfate, high surface area sodium,and the like adsorbents. Similarly, the water content of the chargestock may be adjusted by suitable stripping operations in afractionation column or like device. And in some cases, a combination ofadsorbent drying and distillation drying may be used advantageously toeffect almost complete removal of water from the charge stock. In anespecially preferred mode of operation, the charge stock is dried to alevel corresponding to less than 5 wt. ppm. of water equivalent. Ingeneral, it is preferred to maintain the hydrogen stream entering thehydrocarbon conversion zone at a level of about 10 vol. ppm. of water orless and most preferably about 5 vol. ppm. or less. If the water levelin the hydrogen stream is too high, drying of same can be convenientlyaccomplished by contacting the hydrogen stream with a suitable desiccantsuch as those mentioned above.

In the reforming embodiment, an effluent stream is withdrawn from thereforming zone and passed through a cooling means to a separation zone,typically maintained at about 25° F. to 150° F., wherein a hydrogen-richgas stream is separated from a high octane liquid product stream,commonly called an unstabilized reformate. When the water level in thehydrogen stream is outside the range previously specified, at least aportion of this hydrogen-rich gas stream is withdrawn from theseparating zone and passed through an adsorption zone containing anadsorbent selective for water. The resultant substantially water-freehydrogen stream can then be recycled through suitable compressing meansback to the reforming zone. The liquid phase from the separating zone istypically withdrawn and commonly treated in a fractionating system inorder to adjust the butane concentration, thereby controlling front-endvolatility of the resulting reformate.

The operating conditions utilized in the numerous hydrocarbon conversionembodiments of the present invention are in general those customarilyused in the art for the particular reaction, or combination ofreactions, that is to be effected. For instance, alkylaromatic, olefin,and paraffin isomerization conditions include: a temperature of about32° F. to about 1000° F. and preferably from about 75° F. to about 600°F., a pressure of atmospheric to about 100 atmospheres, a hydrogen tohydrocarbon mole ratio of about 0.5:1 to about 20:1, and an LHSV(calculated on the basis of equivalent liquid volume of the charge stockcontacted with the catalyst per hour divided by the volume of conversionzone containing catalyst and expressed in units of hr.⁻¹) of about 0.2to 10. Dehydrogenation conditions include: a temperature of about 700°F. to about 1250° F., a pressure of about 0.1 to about 10 atmospheres, aliquid hourly space velocity of about 1 to 40, and a hydrogen tohydrocarbon mole ratio of about 1:1 to 20:1. Likewise, typicalhydrocracking conditions include: a pressure of about 500 psig. to about3000 psig., a temperature of about 400° F. to about 900° F., an LHSV ofabout 0.1 to about 10, and hydrogen circulation rates of about 1000 to10,000 SCF per barrel of charge.

In the reforming embodiment of the present invention, the pressureutilized is selected from the range of about 0 psig. to about 1000psig., with the preferred pressure being about 50 psig. to about 600psig. Particularly good results are obtained at low or moderatepressure; namely, a pressure of about 100 to 450 psig.

The temperature required for reforming with the instant catalyst isselected from the range of about 775° F. to about 1100° F. andpreferably about 850° F. to about 1050° F. As is well known to thoseskilled in the continuous reforming art, the initial selection of thetemperature within this broad range is made primarily as a function ofthe desired octane of the product reformate considering thecharacteristics of the charge stock and of the catalyst. Ordinarily, thetemperature then is thereafter slowly increased during the run tocompensate for the inevitable deactivation that occurs to provide aconstant octane product. Due to the higher initial activity of thecatalyst of the present invention, not only is the initial temperaturerequirement lower, but also the average temperature requirement usedwith the instant catalyst system to maintain a constant octane productis typically comparable to an equivalent operation with a high qualityplatinum-rhenium catalyst system of the prior art; for instance, acatalyst prepared in accordance with the teachings of U.S. Pat. No.3,415,737. Moreover, it is a singular feature of the catalyst of thepresent invention that the average C₅ + yield, the C₅ + yield stability,and hydrogen selectivity associated therewith are markedly superiorrelative to those exhibited by this high quality bimetallic reformingcatalyst of the prior art. In effect the present catalyst system enablesa singular shift of the yield-octane curve of the platinum-rheniumcatalyst system towards substantially higher C₅ + yield at similaroctane levels. This last feature of the present invention is ofconsiderable economic significance to the typical petroleum refinerbecause his profit objective is to maximize yield at octane.

The reforming embodiment of the present invention also typicallyutilizes sufficient hydrogen to provide an amount of about 1 to about 20moles of hydrogen per mole of hydrocarbon entering the reforming zone,with excellent results being obtained when about 2 to about 6 moles ofhydrogen are used per mole of hydrocarbon. Likewise, the liquid hourlyspace velocity (LHSV) used in reforming is selected from the range ofabout 0.1 to about 10, with a value in the range of about 1 to about 5being preferred.

The following examples are given to illustrate further the preparationof the attenuated superactive multimetallic catalytic composite of thepresent invention and the use thereof in the conversion of hydrocarbons.It is understood that the examples are intended to be illustrativerather than restrictive.

EXAMPLE I

A tantalum-containing alumina carrier material comprising 1/16 inchspheres was prepared by: forming an aluminum hydroxyl chloride sol bydissolving substantially pure aluminum pellets in a hydrochloric acidsolution, admixing finely divided particles (i.e. 10 to 1000 microns indiameter) of tantalum pentachloride to a solution ofhexamethylenetetramine in an amount sufficient to result in a finishedcatalyst containing about 0.6 wt. % tantalum, vigorously stirring theresulting mixture in order to evenly disperse the tantalum componenttherein, adding the resulting mixture of tantalum pentachloride andhexamethylenetetramine to the alumina sol with sufficient agitation touniformly disperse the tantalum component in the sol, gelling theresulting solution by dropping it into an oil bath to form sphericalparticles of a tantalum-containing alumina hydrogel, aging and washingthe resulting particles, and finally drying and calcining the aged andwashed particles to form spherical particles of gamma-alumina containinga uniform dispersion of about 0.6 wt. % tantalum in the form of tantalumoxide or oxychloride or aluminate and about 0.3 wt. % combinatedchloride. Additional details as to this method of preparing thepreferred gamma-alumina carrier material are given in the teachings ofU.S. Pat. No. 2,620,314.

An aqueous impregnation solution containing chloroplatinic acid andhydrogen chloride was then prepared. The tantalum-containing aluminacarrier material was thereafter admixed with the impregnation solution.The amount of the metallic reagent contained in this impregnationsolution was calculated to result in a final composite containing, on anelemental basis, 0.375 wt. % platinum. In order to insure uniformdispersion of the platinum component throughout the carrier material,the amount of hydrogen chloride used in this impregnation solution wasabout 2 wt. % of the alumina particles. This impregnation step wasperformed by adding the carrier material particles to the impregnationmixture with constant agitation. In addition, the volume of the solutionwas approximately the same as the bulk volume of the alumina carriermaterial particles so that all of the particles were immersed in theimpregnation solution. The impregnation mixture was maintained incontact with the carrier material particles for a period of about 1/2 toabout 3 hours at a temperature of about 70° F. Thereafter, thetemperature of the impregnation mixture was raised to about 225° F. andthe excess solution was evaporated in a period of about 1 hour. Theresulting dried impregnated particles are then subjected to an oxidationtreatment in a dry air stream at a temperature of about 975° F. and aGHSV of about 500 hr.⁻¹ for about 1/2 hour. This oxidation step wasdesigned to convert substantially all of the platinum ingredient to thecorresponding platinum oxide form. The resulting oxidized spheres weresubsequently contacted in a halogen treating step with an air streamcontaining H₂ O and HCl in a mole ratio of about 30:1 for about 2 hoursat 975° F. and a GHSV of about 500 hr.⁻¹ in order to adjust the halogencontent of the catalyst particles to a value of about 1 wt. %. Thehalogen-treated spheres were thereafter subjected to a second oxidationstep with a dry air stream at 975° F. and a GHSV of 200 hr.⁻¹ for anadditional period of about 1/2 hour.

The resulting oxidized, halogen-treated, platinum-andtantalum-containing carrier material particles were then subjected to adry reduction treatment designed to reduce substantially all of theplatinum component to the elemental state and to maintain a uniformdispersion of this component in the carrier material. This reductionstep was accomplished by contacting the particles with ahydrocarbon-free, dry hydrogen stream containing less than 5 vol. ppm.H₂ O at a temperature of about 1050° F., a pressure slightly aboveatmospheric, a flow rate of hydrogen through the particles correspondingto a GHSV of about 400 hr.⁻¹ and for a period of about one hour.

Rhenium carbonyl complex, Re₂ (CO)₁₀, was thereafter dissolved in ananhydrous acetone solvent in order to prepare the rhenium carbonylsolution which was used as the vehicle for reacting rhenium carbonylwith the carrier material containing the uniformly dispersed platinumand tantalum. The amount of this complex used was selected to result ina finished catalyst containing about 0.375 wt. % rhenium derived fromrhenium carbonyl. The resulting rhenium carbonyl solution was thencontacted under appropriate impregnation conditions with the reducedplatinum- and tantalum-containing alumina carrier material resultingfrom the previously described reduction step. The impregnationconditions utilized were: a contact time of about one half to aboutthree hours, a temperature of about 70° F. and a pressure of aboutatmospheric. It is important to note that this impregnation step wasconducted under a nitrogen blanket so that oxygen was excluded from theenvironment and also this step was performed under anhydrous conditions.Thereafter the acetone solvent was removed under flowing nitrogen at atemperature of about 175° F. for a period of about one hour. Theresulting dry rhenium carbonyl impregnated particles were then subjectedto a pyrolysis step designed to decompose the carbonyl compound. Thisstep involved subjecting the carbonyl impregnated particles to a flowinghydrogen stream at a first temperature of about 230° F. for about onehalf hour at a GHSV of about 600 hr.⁻¹ and at atmospheric pressure.Thereafter in the second portion of the pyrolysis step the temperatureof the impregnated particles was raised to about 575° F. for anadditional interval of about one hour until the evolution of CO was nolonger evident. The resulting catalyst was then maintained under anitrogen blanket until it was loaded into the reactor in thesubsequently described reforming test.

A sample of the resulting pyrolyzed rhenium carbonyl, tantalum andplatinum-containing catalytic composite was analyzed and found tocontain, on an elemental basis, about 0.375 wt. % platinum, about 0.375wt. % rhenium derived from the carbonyl, about 0.6 wt. % tantalum andabout 1 wt. % chloride. The resulting catalyst is hereinafter referredto as Catalyst A. For this catalyst the atomic ratio of tantalum toplatinum was about 1.72:1 and the atomic ratio of rhenium to platinumwas about 1:1.

EXAMPLE II

In order to compare the attenuated superactive acidic multimetalliccatalytic composite of the present invention with a platinum-rheniumcatalyst system of the prior art in a manner calculated to bring out thebeneficial interaction of the pyrolyzed rhenium carbonyl component withthe platinum and tantalum components, a comparison test was made betweenthe catalyst of the present invention prepared in accordance withExample I, Catalyst A, and a control catalyst, which was a bimetallicreforming catalyst of the prior art which is similar to the catalystexemplified in the teachings of Kluksdahl's U.S. Pat. No. 3,415,737. Thecontrol catalyst is hereinafter called Catalyst C and was a conventionalcombination of platinum, rhenium and chloride with an alumina which wasprepared by co-impregnation of platinum and rhenium using animpregnation solution containing the required amounts of chloroplatinicacid, perrhenic acid and hydrochloric acid. This control catalystcontained these metals in the same amounts as the catalyst of thepresent invention; that is, the catalyst contained 0.375 wt. % platinum,0.375 wt. % rhenium and about 1.0 wt. % chloride. Catalyst C is thusrepresentative of the platinum-rhenium bimetallic catalyst systems ofthe prior art.

These catalysts were then separately subjected to a high stressaccelerated catalyst reforming evaluation test designed to determine ina relatively short period of time their relative activity, selectivity,and stability characteristics in a process for reforming a relativelylow-octane gasoline fraction. In all tests the same charge stock wasutilized and its pertinent characteristics are set forth in Table I.

This accelerated reforming test was specifically designed to determinein a very short period of time whether the catalyst being evaluated hassuperior characteristics for use in a high severity reforming operation.

                  TABLE I                                                         ______________________________________                                        Analysis of Charge Stock                                                      ______________________________________                                        Gravity, API at 60° F.                                                                           59.1                                                Distillation Profile, °F.                                                Initial Boiling Point   210                                                    5% Boiling Point       220                                                   10% Boiling Point       230                                                   30% Boiling Point       244                                                   50% Boiling Point       278                                                   70% Boiling Point       292                                                   90% Boiling Point       316                                                   95% Boiling Point       324                                                   End Boiling Point       356                                                 Chloride, wt. ppm.        0.2                                                 Nitrogen, wt. ppm.        0.1                                                 Sulfur, wt. ppm.          0.1                                                 Water, wt. ppm.           10                                                  Octane Number, F-1 clear  35.6                                                Paraffins, vol. %         67.4                                                Naphthenes, vol. %        23.1                                                Aromatics, vol. %         9.5                                                 ______________________________________                                    

Each run consisted of a series of evaluation periods of 24 hours, eachof these periods comprises a 12-hour line-out period followed by a12-hour test period during which the C₅ + product reformate from theplant was collected and analyzed. The test runs for the Catalysts A andC were performed at identical conditions which comprises a LHSV of 2.0hr.⁻¹, a pressure of 300 psig., a 3.5:1 gas to oil ratio, and an inletreactor temperature which was continuously adjusted throughout the testin order to achieve and maintain a C₅ + target research octane of 100.

Both test runs were performed in a pilot plant scale reforming unitcomprising a reactor containing a fixed bed of the catalyst undergoingevaluation, a hydrogen separation zone, a debutanizer column, andsuitable heating means, pumping means, condensing means, compressingmeans, and the like conventional equipment. The flow scheme utilized inthis plant involves commingling a hydrogen recycle stream with thecharge stock and heating the resulting mixture to the desired conversiontemperature. The heated mixture is then passed downflow into a reactorcontaining the catalyst undergoing evaluation as a stationary bed. Aneffluent stream is then withdrawn from the bottom of the reactor, cooledto about 55° F. and passed to a gas-liquid separation zone wherein ahydrogen-rich gaseous phase separates from a liquid hydrocarbon phase. Aportion of the gaseous phase is then continuously passed through a highsurface area sodium scrubber and the resulting substantially water-freeand sulfur-free hydrogen-containing gas stream is returned to thereactor in order to supply the hydrogen recycle stream. The excessgaseous phase from the separation zone is recovered as thehydrogen-containing product stream (commonly called "excess recyclegas"). The liquid phase from the separation zone is withdrawn therefromand passed to a debutanizer column wherein light ends (i.e. C₁ to C₄)are taken overhead as debutanizer gas and C₅ + reformate streamrecovered as the principal bottom product.

The results of the separate tests performed on the attenuatedsuperactive catalyst of the present invention, Catalysts A, and thecontrol catalyst, Catalyst C, are presented in FIGS. 1, 2 and 3 as afunction of time as measured in days on oil. FIG. 1 shows graphicallythe relationship between C₅ + yields expressed as liquid volum percent(LV%) of the charge for each of the catalysts. FIG. 2 on the other handplots the observed hydrogen purity in mole percent of the recycle gasstream for each of the catalysts. And finally, FIG. 3 tracks inletreactor temperature necessary for each catalyst to achieve a targetresearch octane number of 100.

Referring now to the results of the comparison test presented in FIGS.1, 2 and 3 for Catalysts A and C, it is immediately evident that theattenuated superactive multimetallic catalytic composite of the presentinvention substantially outperformed the conventional platinum-rheniumcontrol catalyst in the areas of suppression of undesired light gas make(i.e. C₁ to C₄), hydrogen production, average C₅ + yield and C₅ + yieldstability. Turning to FIG. 1 it can be ascertained that the average C₅ +selectivity for Catalyst A was clearly superior to that exhibited forCatalyst C with much better yield stability. The difference in C₅ +yield averaged about 2 vol. % for the duration of the common portion ofthe test and it is clear evidence that Catalyst A has much betteryield-octane characteristics than Catalyst C. Hydrogen selectivities forthese two catalysts are given in FIG. 2 and it is clear from the datathat there is a significant increase in hydrogen selectivity thataccompanies the advance of the present invention; I attribute thisincreased hydrogen selectivity to the moderating effect of tantalum onthe increased metal activity enabled by my unique platinum-rheniumcatalyst system. From the data presented in FIG. 3 it is clear thatCatalyst A possessed an activity characteristic which was comparable tothat possessed by the control catalyst when the two catalysts were runat exactly the same conditions. In sum, the cumulative effect of thedata plotted in FIGS. 1, 2 and 3 indicate that the catalyst system ofthe present invention is surprisingly more selective for C₅ + yield andhydrogen production than the control catalyst and that this dramaticincrease in selectivity is coupled with acceptable activity relative tothe control catalyst.

EXAMPLE III

In order to demonstrate the dramatic effect of tantalum on theplatinum-rhenium carbonyl catalyst system, data is also presented inFIGS. 1, 2 and 3 for Catalyst B which is a platinum-rhenium bimetalliccatalyst in which all of the rhenium component was derived from thepyrolysis of rhenium carbonyl. Catalyst B was manufactured according tothe procedure given in Example I except that a plain alumina carriermaterial was used instead of a tantalum-containing alumina carriermaterial. It is to be understood that Catalyst B is not a prior artcatalyst system but is rather my prior invention as fully described inmy copending application Ser. No. 833,332 filed Sept. 14, 1977.

Catalyst B contained, on an elemental basis, about 0.375 wt. % platinum,about 0.375 wt. % rhenium (derived from pyrolysis of rhenium carbonyl)and about 1 wt. % chlorine. It was subjected to the acceleratedreforming test described in Example II and the results are presented inFIGS. 1, 2 and 3.

Referring to the data in FIGS. 1, 2 and 3 and comparing the results forCatalyst A with those for Catalyst B, it can be discerned that theeffect of tantalum on the platinum-rhenium carbonyl catalyst system ispronounced. This stands in sharp contrast to the effect of tantalum onan ordinary platinum monometallic catalyst system as reported in U.S.Pat. No. 3,799,867. Use of tantalum in the case of my catalyst systemprovides a convenient means to trade-off activity for C₅ + and hydrogenselectivity and allows my superactive platinum-rhenium catalyst systemto be moderated or attenuated in order to adjust the surprisingcharacteristics of this unique catalyst system to applications whereC₅ + yield and hydrogen production are more important than extremelyhigh activity.

In final analysis, it is clear from the data presented in FIGS. 1, 2 and3 for Catalysts A, B and C that the use of a pyrolyzed rhenium carbonylcomponent to interact with a platinum-and tantalum-containing catalyticcomposite provides an efficient and effective means for significantlypromoting an acidic hydrocarbon conversion catalyst containing aplatinum group metal when it is utilized in a high severity reformingoperation. It is likewise clear from these results that the catalystsystem of the present invention is a difference in kind rather thandegree from the platinum-rhenium and platinum-tantalum catalyst systemsof the prior art.

It is intended to cover by the following claims all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in the hydrocarbonconversion art or in the catalyst formulation art.

I claim as my invention:
 1. A catalytic composite comprising acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous carrier material containing a uniformdispersion of catalytically effective amounts of a platinum groupcomponent, which is maintained in the elemental metallic state, and of atantalum component.
 2. A catalytic composite as defined in claim 1wherein the platinum group component is platinum.
 3. A catalyticcomposite as defined in claim 1 wherein the platinum group component isruthenium.
 4. A catalytic composite as defined in claim 1 wherein theplatinum group component is rhodium.
 5. A catalytic composite as definedin claim 1 wherein the platinum group component is iridium.
 6. Acatalytic composite as defined in claim 1 wherein the porous carriermaterial contains a catalytically effective amount of a halogencomponent.
 7. A catalytic composite as defined in claim 6 wherein thehalogen component is combined chloride.
 8. A catalytic composite asdefined in claim 1 wherein the porous carrier material is a refractoryinorganic oxide.
 9. A catalytic composite as defined in claim 8 whereinthe refractory inorganic oxide is alumina.
 10. A catalytic composite asdefined in claim 1 wherein the composite contains the components in anamount, calculated on an elemental metallic basis, corresponding toabout 0.01 to about 2 wt. % platinum group metal, about 0.01 to about 5wt. % tantalum, and about 0.01 to about 5 wt. % rhenium.
 11. A catalyticcomposite as defined in claim 6 wherein the halogen component is presenttherein in an amount sufficient to result in the composite containing,on an elemental basis, about 0.1 to about 3.5 wt. % halogen.
 12. Acatalytic composite as defined in claim 1 wherein substantially all ofthe tantalum component is present in an oxidation state above that ofthe elemental metal.
 13. A catalytic composite as defined in claim 12wherein substantially all of the tantalum component is present astantalum oxide or tantalum oxyhcloride or tantalum aluminate or as amixture thereof.
 14. A catalytic composite as defined in claim 1 whereinthe metals content thereof is adjusted so that the atomic ratio oftantalum to platinum group metal is about 0.1:1 to 10:1 and the atomicratio of rhenium, derived from the rhenium carbonyl component, toplatinum group metal is about 0.5:1 to about 10:1.
 15. A catalyticcomposite as defined in claim 6 wherein the composite contains, on anelemental basis, about 0.05 to about 1 wt. % platinum group metal, about0.05 to about 1 wt. % rhenium, about 0.05 to about 1 wt. % tantalum andabout 0.5 to about 1.5 wt. % halogen.
 16. A catalytic composite asdefined in claim 1 wherein the composite is prepared by the steps of:(a) reacting a rhenium carbonyl compound with a porous carrier materialcontaining a uniform dispersion of a platinum group component,maintained in the elemental metallic state, and of a tantalum component,and thereafter, (b) subjecting the resulting reaction product topyrolysis conditions selected to decompose the rhenium carbonylcomponent.
 17. A catalytic composite as defined in claim 16 wherein thepyrolysis step is conducted under anhydrous conditions and in thesubstantial absence of free oxygen.
 18. A catalytic composite comprisingthe pyrolyzed reaction product formed by reacting a catalyticallyeffective amount of a rhenium carbonyl complex with a porous carriermaterial containing a uniform dispersion of catalytically effectiveamounts of tantalum and of a platinum group metal maintained in theelemental metallic state, and thereafter subjecting the resultingreaction product to pyrolysis conditions selected to decompose therhenium carbonyl component.
 19. A catalytic composite as defined inclaim 18 wherein the porous carrier material contains a catalyticallyeffective amount of a halogen component.
 20. A catalytic composite asdefined in claim 19 wherein the halogen component is combined chloride.